1. Field of the Invention
The present invention relates to an image processing device for decompressing compressed image data. In the device, a general-purpose microprocessor and a specialized circuit cooperate to efficiently decompress the compressed image data, more specifically, the general-purpose microprocessor executes a portion of the data decompression process including a lot of arithmetical and logical operations by software, whereas the specialized circuit carries out a portion of the decompression process including a lot of operations to read out data from a memory.
2. Description of the Related Art
Since image data is considerably large in volume, the data is usually encoded to digital data and further compressed when stored or transmitted. Many studies have been already made especially in relation to encoding and compressing of moving picture data, which results in a standard format of image data for the MPEG (Moving Picture Experts Group) or the like set by the International Organization for Standardization.
Decompression of image data is necessary so as to reproduce an original image data from the compressed image data as represented by moving picture data meeting the MPEG standard. For this purpose, various LSIs for decompression of moving picture data, e.g., HDM8211M (Hyundai Electronics America), M65771FP and M65770FP (Mitsubishi Denki Kabushiki Kaisha), etc. have been developed. The HDM8211M, for example, is described in "Single Chip Performs Both Audio and Video Decoding" (Dave Bursky: pp. 77-80; Electronic Design, Apr. 3, 1995).
Those conventional LSIs require an integrated structure of a lot of operation units, which increases a hardware scale and costs. Further, those LSIs are constructed for a specific purpose and unusable for other uses, therefore, making it necessary to develop LSIs of kinds proportional to the kinds of image data. Thus, the conventional LSIs lack flexibility.
To solve the above-mentioned problem, decompression of image data by software without employing specialized hardware has been tried, whereby some instructions exclusive for processing the MPEG image data are added to a general-purpose microprocessor. The idea is described in "Accelerating Multimedia with Enhanced Microprocessors" (Ruby B. Lee: pp. 22-32; IEEE Micro, April 1995). The decompression process for the MPEG standard image data by software applies an excessive load on the conventional image processing device in spite of a limited operational efficiency or a limited memory access speed of the general-purpose processor. Therefore, the conventional decompression process by software actually achieves low-quality moving picture data or decompresses image data in non-real time, and it is insufficient for decompressing moving picture data in real time with high quality.